This invention relates to golf ball dimple patterns, and, more particularly, to a golf ball dimple pattern which is constructed on a geodesically expanded icosahedron.
In order to provide golf balls with symmetrical, repeatable flight performance, dimple patterns have been developed using spherical projections of polyhedrons, e.g., octahedrons, dodecahedrons, icosahedrons, etc. The dimples are arranged so that the dimple pattern within each polyhedron is the same or substantially the same. Higher numbers of faces or sides on the polyhedron represent higher levels of repeatability. The icosahedron, i.e., a polyhedron with 20 triangular faces, is the most commonly used polyhedron and provides a golf ball with a dimple pattern which has repeating elements composed of 20 spherical triangles.
U.S. Pat. No. 4,560,168 describes an icosahedral dimple pattern. The dimples are positioned within the spherical icosahedral triangles so that the dimples do not intersect the six great circles which pass through the midpoints of the sides of the triangles. The mold parting line can be aligned with one of the great circles, and the other great circles provide false parting lines which increase the symmetry of the pattern.
U.S. Pat. No. 4,142,227 describes a dodecahedral dimple pattern which includes 10 great circles which do not intersect dimples. However, the surface of the ball includes from 12 to 30 rectangular bald patches or dimple-free areas.
The United States Golf Association (USGA) tests golf balls in accordance with a USGA symmetry test. A golf ball is hit by an automatic swinging machine so that it spins about one axis and is then hit so that it spins about an axis which is perpendicular to the first axis. The differences between the two hits should not exceed a certain distance if the ball is symmetrical. If the number of exact repeating elements could be increased, then a dimple pattern could be created with improved symmetry and flight performance repeatability.
British Patent No. 377,354 describes an icosahedral dimple pattern. In FIG. 5 each icosahedral spherical triangle is divided into six right spherical triangles. FIG. 5 does not make any provision for a parting line, and the pattern would be assymetrical at the parting line.
U.S. Pat. No. 4,915,389 also illustrates an icosahedral dimple pattern in which each icosahedral triangle is divided into six right triangles. The pattern does not have any parting line, and the dimples are arranged on all great circles. A spherical surface is formed by a centerless grinding machine, and the dimples are machined into the surface.
U.S. Patent No. 5,192,078 also illustrates an icosahedral dimple pattern in which each icosahedral triangle is divided into six right triangles. Dimples which intersect the mold parting line are removed and replaced with semi-circular or other aerodynamically equivalent dimples which do not intersect the parting line. The pattern might achieve aerodynamic symmetry, but it does not achieve geometric symmetry.
U.S. Pat. No. 5,249,804 describes another icosahedral dimple pattern in which the icosahedral triangles are divided into six right triangles. The parting line is generally sawtooth-shaped and passes back and forth across an equator of the ball.